Stormwater 101

What is stormwater?

Stormwater is simply rain (or snowmelt) that runs across the ground. Stormwater is often called “runoff” because the water runs off, downhill, most often either being absorbed into soil or flowing into a storm drain. You might be asking, how can rain be a problem for us?

Where does stormwater go?

In a natural setting, such as a forest, nearly 40% of rainfall never even touches the ground. It is caught by plant leaves and is either absorbed or evaporates back into the atmosphere. 50% is soaked into the soil, where most is used up by plant roots and the rest slowly percolates into groundwater aquifers after being filtered through the many layers of organic material. In the heaviest rains, only about 10% of rainwater runs off directly into local waterways. This runoff contains very little in the way of pollution and excess nutrients. Historically, nearly all of central Pennsylvania was forested. In developed areas, whether it is an urban landscape, suburban environment, or agricultural field, stormwater runoff acts very differently.

Anywhere from 75-100% of the urban landscape is covered in “impervious surfaces.” Impervious surfaces, such as roofs, driveways, sidewalks, and roadways, are hard surfaces that water cannot pass through. In these urban settings, well over half of rainfall runs off directly into storm drains. The vast majority of storm drains in Pennsylvania, and especially in Blair County, pipe this water directly to local waterways without ever receiving treatment.

Suburban and agricultural environments also have impervious areas not found in the natural environment. Moreover, the turf grass (lawns) and cropping areas of these landscapes differ significantly from forested areas, as does their resulting impact on water quality.

Relationship between impervious cover and surface runoff. Impervious cover in a watershed results in increased surface runoff. As little as 10 percent impervious cover in a watershed can result in stream degradation. Original photo courtesy of Environmental Protection Agency

What are the stormwater-related issues that urban, suburban, and agricultural areas present?

Stormwater basically “rinses off” the landscape, and whatever was on the land prior to a storm event.

In an urban environment, many different sources of pollution can accumulate on roadways and parking lots between storm events. Oil leaking from vehicles, cigarette butts thrown from windows, trash not discarded properly, excess rocksalt applied in the winter, pet waste not cleaned up, and many other dirty items often find their way into storm drains. Many of these pollutants quickly wind up in local streams and waterways. Limiting pollution and retaining water on-site wherever possible is crucial for limiting the negative effects of stormwater runoff in the urban environment.

The suburban environment has some similar threats, but there is also a greater coverage of lawn areas and manicured landscapes. A healthy lawn and garden can absorb stormwater and help prevent runoff issues. Turf grass, however, is limited in the amount of treatment it can provide to water quality. Grass has smaller, shallower root systems than trees or shrubs, meaning it does not absorb as much water as a forest does. Moreover, excess fertilization can introduce additional problems for local waterways. Despite these threats, it’s possible for these landscapes to be both practical for recreation, beautifully designed, and environmentally beneficial.

In agriculture, rainfall plays a critical role in crop success. Many farms have some land that borders or includes small streams, and these waterways are especially at risk for taking on excess nutrients either from fertilizers or from animal waste (cows or horses, for example). Fertilizers, manure management, pesticides, and insecticides all are a critical part of the livelihood of many farmers, and several steps can be taken to make the land both productive and environmentally healthy.

Water and pollutants entering most storm drains goes directly to local streams without treatment. Original photo courtesy of City of Wilmington

What are the signs of stormwater-related issues, and what impact do they have on you?

In many cases, the most noticeable sign that there is a stormwater issue in your area is flooding. Back when Pennsylvania was mostly forested, trees, plants and soils absorbed the majority of rainfall before it reached local streams and rivers. Now, however, much of the rainfall quickly runs off of impervious surfaces directly into rivers. During a large storm, too much water too fast overwhelms these local waterways and results in flooding. This can cause property damage, road closures, and erosion, among other issues.

Another sign is pollution in your local waterways. This pollution may be visible, such as trash, sewage, oil, or murky water (caused by too much erosion). It may also be invisible, caused by toxins, dissolved chemicals, or bacteria and viruses that were swept up by stormwater. Polluted waterways can impact local residents in several ways. You may be unable to swim, play, or fish in the waterway. The river or stream might become an eyesore to passerby. Also, if this waterway is a source of fresh water for your community, additional processes might be required to make it safe to use.

All of these issues have the potential to cause significant environmental impacts to stream ecosystems. Dirt (also called sediment) moved during a flood can cover stream bottoms with soil that prevents trout from spawning, important in-stream insects from breeding, and plant life from receiving sunlight. Excess nutrients from fertilizers cause algae blooms, and when those nutrients make their way downstream, the algae dies off. Through the decomposition process, these water bodies lose much of their dissolved oxygen, which is what fish breathe and need to survive. Pesticides flowing downstream are toxic to many creatures, including mayflies, stoneflies, and caddisflies, which are the main food source for Pennsylvania’s trout populations. Herbicides and other pollutants have the potential to kill off stream plantlife and the trees and shrubs along the streams which hold the banks in place.

How can you make a difference?

Regardless of your role in the community, there are a number of simple and more complicated measures you can take to help improve local water quality and reduce the negative impacts of stormwater! For more information, select Your Role on this website!